In the field of motor apparatus using synchronous motor, a method is known in which a DC bus current of an inverter is detected for reducing the number of electric current sensors detecting three-phase motor current. In this method, in order to appropriately control the motor current, it is desirable to calculate the three-phase motor current from the DC bus current of the inverter, thereby appropriately controlling the magnitude and the phase of the applied voltage to drive the motor.
Patent Literatures 1 and 2 indicated below describe techniques in which a PWM carrier frequency of an inverter is configured to be variable when detecting a DC bus current, thereby improving the detection accuracy of the DC bus current.